Although bone marrow transplantation is currently the treatment of choice for several forms of leukemia and aplastic anemia, this therapy is unavailable for more than 60% of the patients because compatible family donors do not exist. Technological advances in histocompatability testing and improvement in post-transplant care have made it feasible to consider transplants from non-related donors for some patients. Two such transplants have been performed at Milwaukee Children's Hospital within the past year and one was previously undertaken in Seattle. Each was successful. The extreme polymorphism of the HLA system requires large numbers of willing donors to be screened prior to finding one who is potentially compatible. The Blood Center of Southeastern Wisconsin currently maintains a pool of 10,000 active blood donors who are HLA-typed. Recruitment of blood donors as bone marrow donors raises many questions of key importance to a regional blood program. We propose to determine if it is feasible to recruit non-related bone marrow donors from our HLA-types population; whether a pool of 10,000 individuals is sufficient for this task; how the various functions related to recruitment of non-related bone marrow donors should be divided between blood center, hospital and transplant team; the positive and negative effects on the overall blood donor recruitment effort; and the psychological and personal reactions of bone marrow donors, those who decline to donate and those found not compatible. We also propose to recruit donors for patients at the Fred Hutchinson Cancer Center in Seattle and to evaluate the many problems likely to be encountered in sending donors to a distant city. The latter objective is of considerable significance if this therapy becomes more generally available, since donors and recipients will not always reside in close geographic proximity. If successful, it should be possible for our program to be used as a model for recruitment of donors by other blood centers interested in developing this capability.